This invention relates to connectors for coaxial cables and the like, and more particularly, this invention relates to subminiature coaxial connectors (SMA) used for connecting coaxial cable and similar transmission lines at microwave frequencies.
Subminiature coaxial connectors (SMA) are commonly used as high performance subminiature connectors at microwave frequencies. These connectors are used by those skilled in the art with coaxial cables, including flexible and semi-rigid cabling. They are useful up to about 18 GHz with semi-rigid cabling, and with flexible cable, the subminiature coaxial connectors can typically be used from DC values to about 12.4 GHz. In other but more rare cases, they can be specified to operate up to about 18 GHz, but could function mode free up to about 25 GHz. Some subminiature coaxial connectors have been designed to operate up to about 27 GHz in even more rare circumstances.
Subminiature coaxial connectors are operable at broadband frequencies and have low reflections. They are typically designed to have a constant 50 ohm impedance and are constantly used by the microwave industry in many applications where an interface must be made from a coaxial line to a trace or other circuit element printed or otherwise positioned on a circuit board.
These standard subminiature coaxial connectors usually have an outer shell and a screw-thread coupling to ensure uniform contact with outer conductors. In some designs, a snap-fit or press-fit connection is used. In any design, tight coupling enables the subminiature coaxial connectors to minimize reflections and attenuations at high frequencies and provide mechanical strength and durability. Reactances are minimal when there is a tight connection, allowing the subminiature coaxial connectors to be used beyond frequencies associated with other types of snap-on subminiature connectors.
Subminiature coaxial connectors are used with microwave active and passive components, high-end radio electronics, instrumentation applications and avionics. Many different types of subminiature coaxial connectors are commercially available, including connectors from companies such as Light Horse Technologies, Inc., Molex, and Johnson Components, as an example. These connectors are available in pressure crimp, clamp and solder terminal attachments, as an example. They provide adequate connections from printed circuit board strip lines, traces, or other similar circuit elements to coaxial cable. Examples of subminiature coaxial connectors and related plugs are found in U.S. Pat. No. 6,217,382 to Ziers and U.S. Pat. No. 5,823,790 to Magnuson.
Many of the more common subminiature coaxial connectors used today require the use of a solder connection to semi-permanently attach the signal line formed as an electrical conductor or trace printed on a circuit board to the central conductor (or connector) of the subminiature coaxial connector. For example, the central conductor or other connector element centrally positioned within the subminiature coaxial connector would extend into a through-hole positioned in the circuit board at the circuit trace and be soldered thereto. Examples of various subminiature coaxial connectors that require solder connections are SMA right angle solder type plugs for semi-rigid cable, straight jacks, straight plugs, and straight bulk head jacks for semi-rigid cable, solder type antenna connector plugs for flexible or semi-rigid cable, and three-piece plug, jack and bulk head jack. Many other types of subminiature coaxial connector plugs use solder connections.
It is therefore an object of the present invention to provide a subminiature coaxial connector that overcomes the drawbacks of the prior art subminiature coaxial connectors as described above.
It is yet another object of the present invention to provide a subminiature coaxial connector that does not require soldering of the conductor against a circuit board trace or other circuit element and can adjust for relative movements created by thermal mismatch.
The present invention is advantageous and provides a novel and unobvious subminiature coaxial connector and a method of transferring a high frequeny signal in the Gigahertz (GHz) range using the subminiature coaxial connector standard. The present invention allows a low cost and reliable subminiature coaxial connector interface that is aligned normal to the surface of a circuit board and any electrical traces thereon without using a traditional solder processing or through-hole mounts. Thus, the subminiature coaxial connector of the present invention can be attached without subjecting the connector and circuit board to elevated temperatures required for soldering.
The subminiature coaxial connector of the present invention can also be attached to a circuit board without having access to the electrical traces during assembly or processing. The subminiature coaxial connector can be mounted in an inexpensive manner and account for tolerance stack-up, thus allowing a housing (shell) that is less expensive than normal subminiature coaxial connectors because precision machining processes are not required as often required when manufacturing common subminiature coaxial connectors.
The subminiature coaxial connector of the present invention can automatically adjust to relative movements created by thermal mismatch of materials, thus allowing the use of less expensive materials, while decreasing the likelihood of signal degradation because of solder breaks and substrate cracking. It can be used above 3 GHz even when there is a thermal mismatch.
In accordance with the present invention, the connector includes an outer shell. A dielectric is received within the outer shell and includes a longitudinally extending bore. A conductor element is received within the bore and includes an interface contact tip for electrically connecting an electrical circuit, such as a strip line or trace circuit on a circuit board. A biasing element engages the contact tip and biases the interface contact tip into self-adjusting electrical contact against the electrical circuit on the circuit board without soldering. The connector automatically adjusts for relative movement created by thermal mismatch. The outer shell, dielectric and conductor element are preferably formed as a subminiature coaxial connector (SMA). The conductor element further includes a proximal connector opposite the interface contact tip for electrically connecting a coaxial cable using a standard SMA interface connection.
In yet another aspect of the present invention, the biasing element comprises a compliant, spring-loaded intermediate contact. The biasing element can comprise a fuzz button or a pogo pin, in yet another aspect of the present invention. For example, the biasing element could comprise a conductive wool structure, such as a gold plated molybdenum wool that exerts a biasing force, but maintains electrical contact.
In yet another aspect of the present invention, the dielectric and interface contact tip are sized for 50 ohms impedance. The shell can be formed as an SMA shell and be configured for one of a screw-fit, press-fit, or snap-fit connection.